Can a Cavalry unit block an otherwise blockable maneuver attack across a Cavalry Obstructed Approach (say from 11 to 20)? If so how does one handle the following turns assualt assuming no new units are added to the defense?
The way I read the rules the Cav is permitted to block the maneuver attack in spite of the obstruction, but would not be allowed to defend against the future assualt. Assuming the attacker had at least a 2 strength Inf, he would win the assualt. The Cav would not take any damage from the assault, but would take one-step reduction from the retreat. The attacker would also take one-step loss as the winner.
The cavalry could block the maneuver attack. If subsequently assaulted by a 2-strength infantry, the cavalry unit would lose 2, eliminating it. The attacking infantry would also take a loss of 1. The calculation for this is as follows:
2 (the strength of the lead attacking unit) - 1 (the terrain penalty for an infantry assault) - 0 (there are no defense leading pieces, so there is no defense strength to subtract) = +1 (assault strength)
1 (the loss for the defender in any assault) + 1 (the assault strength) = 2 (the defender loss)
1 (the loss for the attacker in any assault)
The cavalry is eliminated, so retreat losses don't apply here anyway, but units do not take retreat losses if they participated in the assault:
"For each approach from which infantry
or cavalry pieces are forced to retreat, a one
strength point loss is assessed. (Exception: if
the retreating pieces were participants in the
assault that caused the retreat, they do not take
additional losses above and beyond what they
suffered in the assault.)"